What 6 to 6.5 actually means
Moonstone sits at 6 to 6.5 on the Mohs hardness scale. Quartz sits at 7, and ordinary household dust contains quartz. That single fact explains almost everything on this page.
It does not mean the stone is fragile to wear. It means the risk is in storage, not on your wrist. A moonstone kept loose in a drawer with other jewelry will pick up fine surface scratches over years, because anything harder than it is grinding against it every time the drawer opens. The same stone worn every day and kept apart from other pieces holds its polish for a long time.
So the single most useful thing you can do is give it its own small space. A pouch, a separate compartment, anywhere it is not touching a faceted stone.
Water
Rain and washing your hands will not hurt the stone.
What the silver would rather avoid is chlorinated pool water and sea water. Both accelerate tarnish on sterling, so it is worth taking the bracelet off before a swim. And neither the stone nor the chain wants to be left soaking wet for long stretches, so dry it if it does get properly wet.
Never polish the coin
This is the one that matters most, because the instinct is exactly wrong.
The coin is oxidized. That dark is not paint or plating sitting on top of the metal, it is a thin layer of silver sulfide grown into the surface, then rubbed back by hand so the high points return to bright silver while the dark stays in the engraved lines. That contrast is what makes the constellation legible at arm's length.
Any polishing cloth or silver dip sold for brightening silver will strip the dark straight out of those lines. The engraving does not come back. What you are left with is a bright disc with barely visible marks on it.
So the coin wants nothing but a dry cloth. And here is the part worth knowing: worn every day, the coin gets better, not worse. Skin and cuff polish the raised surfaces a little brighter each month while the recesses darken, so a coin worn for a year has more contrast in it than a new one. It is a finish improved by use and slightly spoiled by being kept in a box.
Cleaning, when it needs it
A soft dry cloth, or a slightly damp one if there is something on it. Dry it afterward.
That is the whole method. No ultrasonic cleaners, which shake stones loose from settings. No steam. No commercial jewelry dip, for the reason above. Moonstone can also be sensitive to sudden temperature change, so warm water rather than hot.
Everyday habits
Take it off for anything with impact or grit. Hardness measures resistance to scratching and says nothing about resistance to a knock, and a knock on the edge of a stone is what chips it.
Put it on last, after lotion and perfume have dried.
If something breaks
Write to jason@atlasvaelo.com and tell me what happened. Atlas Vaelo is one person, so an answer can take a few days, but nothing goes unread.